Radiofrequency Ablation Electrode Research Articles

Finite element analysis of tissue deformation with a radiofrequency ablation electrode for strain imaging

Recent studies have shown that radiofrequency (RF) electrode displacement or deformation-based strain imaging can be used as an alternate imaging modality to monitor and to evaluate ablative therapies for liver tumors. This paper describes a biomechanical model used to study RF electrode deformation-based strain imaging, in conjunction with a simulated medical ultrasound linear array transducer. The computer simulations reported here are important steps toward understanding this biomechanical system in vivo, thus providing a basis for improving system design, including the motion tracking algorithm and image guidance for performing RF electrode displacement-strain imaging in vivo.

Double radiofrequency ablation is more extensive with a spherical zone shape compared to single ablation in a pig liver model

We compared the duration of ablation and the area of coagulation necrosis between a single ablation method (SAM) and a double ablation method (DAM) with a 'multitined expandable' electrode (LeVeen 2 cm) for radiofrequency ablation (RFA) using pig liver. In the SAM group, ablation was completed after the first roll-off. In the DAM group, an additional ablation was performed to achieve a second roll-off. The comparison was made of the time required for roll-off and the extent of coagulation necrosis between the both groups. The Ellipticity index (EI) quantitatively describes the shape of the general RF ablation zone in the axial plane. There was no statistically significant difference in the interval until the first roll-off between both groups (SAM group: 100.7+/-24.7 seconds vs DAM group: 103.2+/-37.7 seconds, P=0.43). In the DAM group, the interval from the start of the additional ablation until the second roll-off was 154.0+/-86.9 seconds, longer than the interval for the first roll-off (P=0.023). The extent of coagulation necrosis was significantly more extensive in the DAM group (axial diameter, mean+/-SD, 26.2+/-2.8mm) x (maximal diameter: 29.3+/-1.6mm) x (minimal diameter: 26.5+/-3.6mm) compared to the SAM group with (23.0+/-3.3mm) x (23.7+/-3.1mm) x (20.0+/-2.5mm), respectively. Although there was no statistically significant difference in the EI between both groups, macroscopically, the shape of coagulation necrosis tended to be non-spherical in the SAM group and spherical in the DAM group. The DAM with a 'multitined expandable' electrode was more extensive with a spherical zone shape compared to the SAM.

Comparison of expandable electrodes in percutaneous radiofrequency ablation of renal cell carcinoma

Objective To compare two different expandable electrodes in radiofrequency ablation of renal cell carcinoma. Methods Percutaneous ablation was performed at two centers using either an expandable 7F umbrella-shaped LeVeen™ probe (diameter 2–4 cm) and a 200-W generator (group A), or an expandable Starburst XL™ electrode with a 150-W generator (group B). From each center, eight patients with one tumor each were matched retrospectively with regard to tumor volume, which was 9.71 ± 6.43 cm 3 for group A and 8.74 ± 4.35 cm 3 for group B (mean tumor diameter: 2.47 ± 0.9 cm versus 2.50 ± 0.4 cm, respectively). An unpaired t-test showed no significant difference in tumor volume between the two groups ( p = 0.820). Results Sixteen patients with 16 tumors were treated. The primary technical success of radiofrequency ablation was 94% (15 of 16 patients). After retreatment of residual tumor in one patient from group B, secondary technical success was 100%. No major complications were observed. The resulting mean volume of the almost spherical necroses was 21.1 ± 9.1 cm 3 versus 14.6 ± 6.7 cm 3 for groups A and B (diameter of necrosis: 3.5 ± 0.7 cm versus 3.1 ± 0.6 cm, respectively). A Mann–Whitney U-test showed no significant difference in necrosis volume between the two groups (CI [−0.215; 0.471]; p = 0.2892). The calculated shape value of S (ratio of length to height of the coagulation necrosis) was 0.9 ± 0.1 and 1.0 ± 0.1 for groups A and B, respectively. No local recurrence was observed during a mean follow-up of 14.8 ± 11.6 months, while extrarenal tumor progression occurred in three patients. Conclusions No significant differences in coagulation volume and shape were found after RF ablation of renal cell carcinoma using two different expandable electrodes. To avoid local recurrence, however, accurate placement of probes and appropriate expansion of the electrode is necessary.

WE‐C‐330A‐06: FEA and Phantom Tests of Ultrasound Temperature Maps During Thermal Therapy

Purpose: The ability to noninvasively monitor heating patterns during radiofrequency ablation therapy would provide invaluable guidance to clinicians during these procedures. We are investigating ultrasonically recorded and scaled “apparent tissue displacements”, caused by sound speed changes and tissue expansion, for generating temperature maps during ablation. This paper reports FEA simulations and experiments in novel phantoms to determine whether ultrasound can successfully record temperatures. Method and Materials: FEA models were applied to determine the temperature distribution from a radiofrequency ablation electrode in liver. FEA analysis enabled creation of both temperature and tissue expansion maps during simulated procedures. The expansion maps in turn were combined with sound speed changes and used to model ultrasound echo data at intervals during the ablation. In addition, experimental data were acquired using a reusable slurry phantom with embedded sensors surrounding an ablation electrode. Frames of echo data were acquired using a linear array transducer during a 15‐minute heating sequence. For both simulated and real data, two‐dimensional cross‐correlation of echo signals from successive frames yielded accumulated tissue displacements. Scaled gradients of these displacements estimate local temperatures. Results: Temperature maps generated from simulated echo signals correspond well to the underlying temperature maps created with FEA. The zone of elevated temperatures can be easily visualized on these maps. Isothermal curves on the temperature maps may be useful in determining areas that may have incurred cell death or tissue necrosis. Preliminary results indicate good correlation between fiber optic temperature sensor measurements and ultrasound temperature measurements over 1cm2 ROI's surrounding the probe. Conclusion: Temperature maps estimated using ultrasound signals correspond well to the FEA generated temperature maps. Temperature mapping can therefore be used to visualize the zone of heating during a radiofrequency ablation procedure. This result is confirmed by temperature measurements done in an ultrasound phantom.

WE‐C‐330A‐07: Radiofrequency Ablation Electrode Displacement Elastography

Purpose: Elastography can be used to image the position and location of thermal lesions created using radiofrequency (RF) ablation. A challenge, however, when applying this technique to guide treatment of liver tumors is that of producing a controlled compression of the tissue. We are testing a new method, ‘electrode displacement elastography’, for producing elasticity images of ablation therapy treatments. This paper presents results of tests in a custom elastography phantom. Method and Materials: An elastography phantom containing a stiff inclusion (50 kPa) embedded in a soft (11kPa) background was used. A discarded RF electrode was mounted firmly into the inclusion with the handle extending outside the phantom container. A stepper motor applied small (0.1mm) displacements while the phantom was imaged using an ultrasound machine equipped with a research interface, acquiring raw echo data before and after small perturbations of the electrode. One‐dimensional cross correlation was used to estimate displacements. Finite element analyses were also performed to characterize the contrast‐transfer efficiency (CTE) of the conversion from the underlying modulus domain to the observed strain domain. Results: On elastograms the inclusion has a characteristic halo appearance, similar to that observed in in‐vivo tests of this technique. Strain contrast is consistently higher than the underlying modulus contrast, confirmed by a study of the CTE. On simulated strain images, stiffer inclusions in softer backgrounds have CTE values in excess of 0 dB. Conclusions: Feasibility of electrode displacement elastography is shown. The strain contrast observed exceeds the underlying modulus contrast, for stiffer inclusions. This characteristic of the method may provide RF ablation practitioners with added lesion contrast in situations where the actual stiffness ratio between the lesion and surrounding normal tissue is not significantly greater than 1:1.This work is supported by Whitaker Foundation grant RG‐02‐0457.

276 Internally cooled versus perfused electrodes for radiofrequency ablation (rfa) in patients with small (≤3 CM) hepatocellular carcinoma (HCC)

276 Internally cooled versus perfused electrodes for radiofrequency ablation (rfa) in patients with small (≤3 CM) hepatocellular carcinoma (HCC)

Pediatric Return Electrodes for Radiofrequency Ablation in Children

Pediatric Return Electrodes for Radiofrequency Ablation in ChildrenPaul R. Morrison1, Stephen D. Brown2 and Eric vanSonnenberg3Audio Available | Share

Saline‐Irrigated Radiofrequency Ablation Electrode with External Cooling

Open flush, irrigated ablation electrodes may improve the safety of radiofrequency catheter ablation by preventing protein aggregation and coagulum formation. This is particularly important in left-sided procedures like catheter ablation of atrial fibrillation. Electrode cooling and the inherent loss of temperature feedback, however, grossly reduce the ability to monitor tissue heating. Intimate contact may not be recognized and the delivery of nominal RF power levels may then lead to excessive tissue heating, steam explosions, and even tamponade. Standard, open flush, irrigated catheters (Sprinklr, Medtronic Inc, Minneapolis, MN) were modified by thermally insulating the irrigation channels inside the ablation electrode. Using the thigh muscle preparation, multiple lesions were created with standard and modified catheters using 60 s, 20-50 Watt applications and a constant saline flush rate of 20 cc/min. A total of 57 lesions were created on five thigh muscles of three dogs. Lesion dimensions were not significantly different between both types of catheter, but the maximum electrode temperature rise during ablation was significantly higher with the modified catheter. Insulation of the irrigation channels improved the correlation coefficient between maximum electrode temperature rise and lesion volume from 0.38 (ns) to 0.62 (P < 0.001). Thermal insulation of the irrigation channels facilitates temperature feedback during radiofrequency ablation and controllability of lesion formation.

Treatment of hepatocellular carcinoma with percutaneous radiofrequency ablation: usefulness of contrast harmonic sonography for lesions poorly defined with B-mode sonography.

The purpose of this study was to assess the usefulness of contrast harmonic sonography guidance in percutaneous radiofrequency ablation of hepatocellular carcinomas that could not be adequately depicted by B-mode sonography. SUBJECTS AND METHODS. Twenty-one patients with 21 hepatocellular carcinomas prospectively underwent radiofrequency ablation treatment with contrast harmonic sonography as guidance. Twenty-five patients with 25 hepatocellular carcinomas were retrospectively selected as the historical control group under the same conditions as the study group; the control group patients were treated under B-mode sonography guidance. Twenty (95.2%) of the 21 patients were successfully treated during a single treatment session, and the remaining patient (4.8%) required two treatment sessions with contrast harmonic guidance. On the other hand, only eight (32%) of the 25 control subjects were successfully treated during a single treatment session using B-mode sonographic guidance without contrast imaging. The difference between these two groups was statistically significant (p = 0.002). Contrast harmonic sonography helps in the placement of radiofrequency ablation electrodes in hypervascular hepatocellular carcinomas that cannot be adequately depicted by B-mode sonography.

Magnetic Resonance Imaging Characteristics of Six Radiofrequency Electrodes in a Phantom Study

To evaluate and compare visibility and artifacts in magnetic resonance (MR) compatible radiofrequency (RF) electrodes for MR-guided RF ablation. Six different MR compatible electrodes for RF ablation including two internally cooled single needles, one internally cooled cluster needle, two expandable needles and one perfused needle were tested in a phantom study at 0.2 Tesla and at 1.5 Tesla field strength. Fluoroscopic, T1- and T2-weighted fast spin echo (FSE) and gradient echo (GE) sequences, which are usually used for MR-guided interventions, were evaluated. Qualitative and quantitative evaluations were performed. Length, width, noise, tip artifacts, global artifacts and global visualization of the RF electrodes that showed all sequences at different angles. Qualitative analysis showed that electrodes were well visualized at all angles and sequences and on both MR imagers. Quantitative analysis showed that artifact-induced widening of the shaft was increased in all electrodes by: a). use of fluoroscopic sequences, GE sequences, and fat saturation, b). increasing the angle between the needle and main magnetic field, and c). high field strength (1.5 T). Expandable needles produced fewer tip artifacts but broader signal voids along the shaft compared to nonexpandable needles. Cluster electrodes produced less widening than the other electrodes. Visibility and artifacts in all six MR compatible RF electrodes are satisfactory and these electrodes could be used for MR-guided radiofrequency ablation procedures.

Bipolar saline-enhanced electrode for radiofrequency ablation: results of experimental study of in vivo porcine liver.

To evaluate whether a bipolar saline-enhanced radiofrequency (RF) ablation system embedded in one needle is able to consistently produce homogeneous and predictable areas of coagulation necrosis with or without the Pringle maneuver of vascular inflow occlusion. RF ablation (480 kHz) of the liver was performed in 24 healthy pigs by means of laparotomy: group A (n = 5), 4-cm distance between electrodes 1 and 2; group B (n = 7), 4-cm distance and the Pringle maneuver; group C (n = 5), 2-cm distance; and group D (n = 7), 2-cm distance with the Pringle maneuver. Twenty percent NaCl solution was infused continuously at a rate of 100 mL/h via each electrode during the procedure. The pigs were followed up, and they were euthanized on the 7th day. Livers were removed for histologic assessment. Time, impedance, current, power output, specific voltage of the contacts, energy output, temperatures in the liver, volume of the lesion, and energy delivered per lesion volume were determined and compared among groups. Predictability of lesion volume was evaluated with the coefficient of variability. Mean values of the variables were compared among the groups by means of one-way analysis of variance or Kruskall-Wallis test. Impedance at the end of the RF ablation procedure was almost twofold lower than the corresponding initial value in all groups. In Pringle groups B and D, regular ellipsoids of coagulation necrosis were created (mean lesion volume, 149.50 cm3 +/- 34.26 and 69.43 cm3 +/- 15.48, respectively). In non-Pringle groups A and C, the shape of coagulation necrosis was influenced by the vessels encountered, and mean lesion size was lower than that in the Pringle groups (P <.01). The coefficient of variability of lesion size was lower in the Pringle groups (23% and 22%, respectively) than that in the non-Pringle groups (75% and 30%, respectively). The bipolar saline-enhanced RF ablation method produces homogeneous and predictable areas of coagulation necrosis between two electrodes, regardless of the distance between them, preferably with vascular inflow occlusion.

Long electrodes for radio frequency ablation: comparative study of surface versus intramural application

There is increasing use of radio frequency (RF) ablation with long electrodes in the intraoperative treatment of atrial fibrillation. Nevertheless, the disparity in the lesion geometry in both depth and width is the major pitfall in the use of RF currents. The objective of this study was to differentiate the shape and size of long lesions created by three surface application electrodes (SAE) and two intramural electrodes (IE). The SAE included a standard multi-polar catheter, and two standard electrosurgical pencils. The IE consisted of a needle and a wire both intramurally buried. The lesions were created on fresh fragments of porcine ventricular tissue. The IE created lesions with a curved prism-like shape around the electrode body, with homogeneous characteristics along the lesion trajectory. On the contrary, the lesions created with the SAE were in the shape of an hourglass. They showed a different geometry between the central zone and the edge zone ( p<0.001 for depth and surface width). Electrical impedance evolution was recorded during the RF heating. We observed a slow decrease of the impedance in all the electrodes, except in the wire electrode. In conclusion, the results suggest that the IE might be a more suitable option than SAE when it is necessary to create long and homogeneous thermal lesions.

Tumor seeding complicating radiofrequency ablation of hepatocellular carcinoma

A 77-year-old woman with cryptogenic cirrhosis presented with a 3 cm contrast enhancing mass in the lateral segment of the left hepatic lobe seen on triphasic computed tomographic (CT) examination of the abdomen. Her alpha fetoprotein (AFP) was 48.4 ng/ml (<6 ng/ml). An ultrasound guided transcutaneous single pass radiofrequency ablation (RFA) of the mass was performed without immediate complications. Seven months later the patient presented with upper abdominal pain. A repeat CT scan demonstrated a new lobulated contrast enhancing mass in the subcutaneous fat of the midline anterior abdominal wall (white arrow). A 3 cm hypodense area in the lateral segment of the left hepatic lobe (black arrow), consistent with the site of previous RFA, was also observed. The repeat serum AFP was now 999 ng/ml. The subcutaneous mass represents needle tract seeding complicating the RFA. RFA is a thermal treatment technique designed to produce localized tumor destruction. Its use is particularly attractive in high-risk operative candidates such as our elderly patient with a localized HCC in a cirrhotic liver. RFA can be performed percutaneously, laparoscopically or at the time of laparotomy. Treatment related complications occur in 10% of patients in most series and include pain, hemoperitoneum, capsular hematoma, pneumothorax, infection and portal thrombosis. Local tumor recurrence at the RFA site is infrequent (3.6%) [[1]Curley S.A. Izzo F. Ellis L.M. Vauthey J.N. Vallone P. Radiofrequency ablation of hepatocellular cancer in 110 patients with cirrhosis.Ann Surg. 2000; 232: 381-391Crossref PubMed Scopus (703) Google Scholar]. Needle tract seeding, in up to 12.5% of cases, is now also recognized as a long-term complication of RFA [[2]Llovet J.M. Vilana R. Bru C. Bianchi L. Salmeron J.M. Boix L. et al.Increased risk of tumor seeding after percutaneous radiofrequency ablation for single hepatocellular carcinoma.Hepatology. 2001; 33: 1124-1129Crossref PubMed Scopus (668) Google Scholar]. This particular complication occurs predominantly in surface or immediate subcapsular lesions such as in this patient. Proposed explanations include the larger needles used in RFA compared with other forms of local therapy such as percutaneous ethanol injection. The J-hooks used in the multiple array RFA electrodes can also potentially pierce the capsule in peripheral tumors resulting in local seeding. This case highlights the risk of tumor seeding after RFA of subcapsular HCC.

A novel "cooled-wet" electrode for radiofrequency ablation.

In the light of growing demands for improved applicability of radiofrequency ablation (RFA), recently we have developed a novel "cooled-wet" electrode by taking the advantages of both internally cooled and saline-enhanced electrodes. The efficacy of the electrode was evaluated in both ex vivo and in vivo liver RFA under both low and high power output levels. The ablation volume created with the "cooled-wet" electrode appeared to be much larger than that reported up to now with the use of other monopolar electrodes. The mechanisms on how this device optimizes the RF energy delivery are also discussed.

Finite element analyses of uniform current density electrodes for radio-frequency cardiac ablation.

The high current density at the edge of a metal electrode causes hot spots, which can lead to charring or blood coagulation formation during radio-frequency (RF) cardiac ablation. We used finite element analysis to predict the current density distribution created by several electrode designs for RF ablation. The numerical results demonstrated that there were hot spots at the edge of the conventional tip electrode and the insulating catheter. By modifying the shape of the edge of the 5-mm tip electrode, we could significantly reduce the high current density at the electrode-insulator interface. We also studied the current density distribution produced by a cylindrically shaped electrode. We modified the shape of a cylindrical electrode by recessing the edge and filled in a coating material so that the overall structure was still cylindrical. We analyzed the effects of depth of recess and the electrical conductivity of the added material. The results show that more uniform current density can be accomplished by recessing the electrode, adding a curvature to the electrode, and by coating the electrode with a resistive material.

A new catheter design using needle electrode for subendocardial RF ablation of ventricular muscles: finite element analysis and in vitro experiments.

Radio-frequency (RF) cardiac ablation has been very successful for treating arrhythmias related with atrioventricular junction and accessory pathways with successful cure rates of more than 90%. Even though ventricular tachycardia (VT) is a more serious problem, it is known to be rather difficult to cure VT using RF ablation. In order to apply RF ablation to VT, we usually need to create a deeper and wider lesion. Conventional RF ablation electrodes often fail to produce such a lesion. We propose a catheter-electrode design including one or more needle electrodes with a diameter of 0.5-1.0 mm and length of 2.0-10 mm to create a lesion large enough to treat VT. One temperature sensor could be placed at the middle of the needle electrode for temperature-controlled RF ablation. From finite element analyses and in vitro experiments, we found that the depth of a lesion is 1-2 mm deeper than the insertion depth of the needle and the width increases as we increase the diameter of the needle and the time duration. We showed that a single needle electrode can produce a lesion with about 10-mm width and any required depth. If a wider lesion is required, more than one needle with suggested structures can be used. Or, repeated RF ablations around a certain area using one needle could produce a cluster of lesions. In some cases, a catheter with both conventional electrode and needle electrode at its tip may be beneficial to take advantage of both types of electrode.

Efficacy of multiple ring and coil electrode radiofrequency ablation catheters for the creation of long linear lesions in the atria

Atrial fibrillation is an arrhythmia that may potentially be treated by creating long linear lesions in the atria to create lines of electrical conduction block. While this has been performed with success with open-heart surgery, it has been proposed that a less invasive catheter-based approach could achieve similar success. Radiofrequency energy catheter ablation was performed in vivo with two novel electrode catheters. Each was an expanding loop design: one with 3 mm ring electrodes; and one with 12.5 mm coil electrodes. Power delivery was controlled automatically with temperature (70°C target) feedback from thermistors embedded in each electrode. A total of 39 lines of ablation were created in the atria of 11 normal dogs. The coil electrodes were more effective in creating lesions than the ring electrodes with a similar prevalence of transmurality (89% vs. 85%) but a higher prevalence of continuous transmurality (35% vs. 5%). Sequential electrode energy delivery was better than simultaneous multipolar delivery due to varying efficiencies of tissue heating. Inadequate heating was observed in 47% of simultaneous versus 1% of sequential multipolar deliveries, and excessive heating in 6% versus 1% of cases, respectively. It is feasible to create linear atrial lesions with an expanding loop electrode catheter. Catheters with coil electrodes are more effective than those with ring electrodes. In order to avoid coagulum formation and inefficient heating, sequential electrode energy delivery is preferable to multipolar delivery.